1. Field of the Invention
The present invention relates to a method for fabricating a thin film bulk acoustic resonator (FBAR) which may be used as a filter used for electronic circuits and more particularly to the method having simple steps to fabricate the FBAR, besides having high production ability of the FBAR.
2. Description of Related Art
The high frequency and exact resonance frequency of the FBAR are important elements when fabricating the FBAR. The earlier generation SAW (surface acoustic wave) fabricating method of a resonator employed a pair of parallel fingers on a surface of a substrate. To fabricate a high frequency by the conventional method, a distance of the two adjacent metal fingers has to be reduced. For example, a resonator having 2 GHz frequency is able to use a semiconductor process with less than 0.5 xcexcm. Therefore, fabricating the high frequency resonator is costly and owing to use the surface acoustic property. The power handling is another major limitation for high performance wireless product.
A present resonator adopting the surface acoustic wave theory is able to solve the above drawbacks incurred in the conventional processing of the resonator. The resonator is fabricated according to the surface acoustic wave theory to have a high frequency and high power factor. That is, a direction of the acoustic wave of the resonator and a surface of the resonator are perpendicular to each other, whereby the resonator needs a relationship of some important elements such as the piezoelectric material and the working frequency of the resonator are inverse proportion to each other, to fabricate an FBAR.
With reference to FIGS. 6A to 6E, a conventional fabricating method of a thin film bulk acoustic resonator (FBAR) is shown. The method for fabricating the resonator comprises the following steps:
defining a recess (501) in a top face of a Si substrate (50) and then applying a SiO2 layer (51) on the top face of the Si substrate;
applying a phosphorsilica glass layer (52) on the SiO2 layer (51);
chemical machine polishing the phosphorsilica glass layer (52) to have a portion of the phosphorsilica glass layer (52) remained in the recess (501);
sequentially forming a first conductive layer (53), a piezoelectric material layer (55) and a second conductive layer (54) on the phosphorsilica glass layer (52) remained in the recess (501); and
etching away the phosphorsilica glass layer (52) to expose the recess (501).
As per the above steps, a resonator is formed on the recess (501), that is, after the phosphorsilica glass layer (52) is etched, the body of the resonator is supported by the edge of the recess (501). However, the substrate (50) corresponding to the body of the resonator has to define the recess (501) for having high frequency filtering ability, so that, before forming the body of the resonator, the recess (501) has to undergo filling and polishing steps. Therefore, the above complex steps are necessary for the conventional resonator to be able to have high frequency and high power factor, and thus fabricating the FBAR not only takes considerable time but also has a slow production rate.
To overcome those shortcomings, the present invention provides simple and easy steps and good production ability to mitigate and obviate the aforementioned problems.
The objective of the present invention is able to provide a simple method for fabricating thin film bulk acoustic resonators (FBAR), and furthermore, the fabrication method of the FBAR does not need a chemical machine polishing(CMP) step. The method for fabricating FBAR comprises the following steps:
preparing a Si substrate;
applying an insulating layer on the Si substrate;
sequentially applying a first conductive layer, a piezoelectric material layer and a second conductive layer on top of the Si substrate;
partially etching the second conductive layer and the piezoelectric material layer to form an upper electrode and a piezoelectric layer; and
defining holes in the first conductive layer by etching so as to allow the formation of a chamber under the first conductive layer.
Therefore, fabricating the FBAR requires only a short working time, and the production rate of the FBAR is accordingly high.
Other objects, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.